1. Field of the Invention
The present invention relates to a method of producing a resin molded article composed of a surface layer and a base material of a synthetic resin formed as one body, wherein joining between the end of the surface layer and the base material is improved.
2. Description of the Related Arts
A resin molded article has been used for automotive trim parts such as an instrument panel (a dashboard), furniture such as a chair, etc., which is composed of a synthetic resin as a base material and a surface layer of a synthetic leather, provided on the surface of the base material.
The abovementioned resin molded article is designated by the numeral 9 in FIGS. 19 and 20. A surface layer 90 composed of a sheet 91 and a foam layer 92 is molded on the surface of a base material 93 which is made of a synthetic resin and has a U-like configuration in cross section as one body. An end portion 901 of the surface layer 90 is bent inwardly and fixed to the back of the base material 93. Tacks, ultrasonic bonding, an adhesive, etc. can be used to fix the end portion. The numeral 94 designates a rib.
The abovementioned resin molded article 9 has been produced by so-called stamping molding as shown in FIGS. 13 through 15. In molding the abovementioned resin molded article, a heated molten synthetic resin 930 is put on a mold surface 811 of a lower mold portion 81 as a base material and the surface layer 90 is disposed thereon. Then, an upper mold portion 82 is lowered on to the lower mold portion so as to press and mold the aforesaid molten synthetic resin 930 and the surface layer 90 (see FIG. 14). Thereafter, a molded article composed of the synthetic resin 93 and the surface layer 90, which are joined as one body, can be obtained by cooling to cure it.
In this molded article, the end portion 901 of the surface layer 90 is bent toward the back of the end portion 931 of the base material 93, and is fixed thereto as described above. Thus, a resin molded article as shown in FIG. 20 is obtained.
However, in the abovementioned conventional method, bent portion A has a large radius of curvature because the surface layer 90 has a foam layer 92. Thus the outward appearance is deteriorated. Further, fixing of the end portion 901 bent inwardly toward the back of the end portion 931 is difficult because of the hard elastic restitution of the foam layer as described above. So, in this bending process, a specific jig for bending is required to fix the end portion 901 to the base material 93 by tacks, an adhesive, etc.
When a burr (or a flash) 93 is formed on the end portion 931 of the base material 93 in molding as shown in FIG. 16, the radius of curvature of the bent portion A is greater.
There is another method as shown in FIG. 17 wherein the surface layer 90 is not bent toward the back of the base material 93. In this case, however, the thickness of the end portion 931 of the base material 93 is very thin, about 2 to 3 mm. So, when the surface layer having elasticity is fixed on such a short distance, the end portion 901 of the surface layer is easily separated from the base material 93.
Then, though it is possible for the thickness of the end portion 931 of the base material 93 to be greater, i.e. 5-6 mm, the synthetic resin of the base material 93 is deformed portion and warpage C occurs as shown in FIG. 18. A sink mark appears in molding and the outward appearance is deteriorated.
As described above, many processes have been necessary to dispose of the end portion 901 of the surface layer 90 in the conventional method of producing a resin molded article having a surface layer. In particular, when the end portion 931 of the base material 93 has a complex convexo-concave shape or a three-dimensional shape, more processes to dispose of the end portion have been required.